Royal Dutch Shell is facing calls to publish its latest inspection report for
the North Sea pipeline where it is still battling an oil leak.

The energy giant has now managed to send divers down to inspect the source of the oil, which is believed to be oozing less than one barrel per day into the ocean.

Current estimates suggest around 1,300 barrels have escaped into the water, with the potential for a further 4,000 barrels to emerge from the isolated pipeline leading from the well to its Gannet Alpha platform.

Yesterday, it laid concrete weights known as "rock mattresses" to secure the pipeline to the seabed. It has also been conducting air surveillance to monitor bird and marine wildlife. According to Shell's latest estimates, the sheen of oil on the surface of the sea is 500 metres by 500 metres.

Calls for the company to release its inspection report came from the Royal Society for the Protection of Birds (RSPB), as it emerged that the first oiled bird has been spotted in the area.

However, Shell is insisting that there has been "no significant impact on the environment" and believes the spill will be over in "days rather than weeks".

Despite this claim, commentators around the world have begun to question the company's plans to drill in difficult conditions.

Frances Beinecke, president of the Natural Resources Defense Council, who sat on the presidential inquiry into BP's Gulf of Mexico oil spill, argues in the New York Times that Shell should not be allowed to drill in the Arctic.

"We need containment and response plans tailored to the demands of marine operations under some of the most unforgiving conditions anywhere on earth," she wrote.

"And we must be realistic about the kind of backup available in a place 1,000 miles from the nearest US Coast Guard station.

"Shell's latest spill, in the North Sea, reminds us of the peril we court by ignoring these urgent needs."

New Zealand media have also raised concerns about the North Sea oil spill, after Shell took shares in deepwater offshore exploration blocks recently.

Separately, BP confirmed it has been asked to investigate an oily sheen in the Gulf of Mexico, near to two of its abandoned wells. Other operators nearby have also been asked to examine their infrastructure.